In ball sports requiring a hitting tool to play them, it is well known that significant shock impulses and resonant vibrations occur as a reaction to the impact of the hitting tool with the ball. The distinct vibrations represent a considerable risk of injury for the arm, the shoulder and the spine of the player. For example, there is the so-called tennis elbow condition, in which, due to the vibration of the racquet, a significant local increase of tissue metabolism occurs along with leukocyte migration in the tissue. Tennis elbow is observed very frequently and causes great pain for a tennis player.
Conventional tennis racquets tend to have disadvantageous vibration behavior after impacting the ball, producing especially large impulses of energy. The design of known tennis racquets is such that an amplitude maximum occurs in the handle, and thus in the hand of the player.
German utility model specification DE 29805032 U1 describes a racquet frame for a tennis, badminton or squash racquet. The known frame is made from a single, tubular fiber-reinforced plastic. The tubular plastic part has an elliptical cross section, the longitudinal sides of which are connected to one or two cross members thus forming chambers within the single plastic part.
With two ribs, a center chamber is formed that holds a foam element. Due to the elliptical shape of the cross section, the plastic part has its largest width at its center, through which the strings of the webbing pass via holes. This results in the mass being concentrated mostly in the center.
Furthermore, in the American patent specification U.S. Pat. No. 5,516,100, a frame for a tennis racquet is known which is bent from a single tubular profile element that has the cross sectional shape of a bean. Within the single profile element is a stiffening rib that connects the two longitudinal sides of the bean-shaped cross section. A string guide strip is embedded in the stiffening rib, providing sleeves through which to feed the strings of the webbing.
AT 388 106 describes a frame for ball racquets that is designed from a center strip and hollow profiles attached to both sides of the middle strip. The middle, strip consists of a thermoplastic, Duroplast, an elastomer, rubber, ceramic, wood, metal, or similar material.
U.S. Pat. No. 4,357,013 describes a structure for a tennis racquet frame that is designed from two outer members with a honeycomb structure and a core lying between them. A common covering encloses the two members and the core. The core is made from a plastic sheet rolled into a spiral and layered.
The frame designs described above according to the state of the technology result in disadvantageous vibration behavior of the racquet when the ball impacts the webbing or the frame itself, with the vibration behavior leading to bodily injury such as tennis elbow.
Therefore, the objective of this invention is to design a structural member for the manufacture of sports equipment, in particular a sports hitting tool such as tennis, squash and badminton racquets, golf clubs, field hockey and ice hockey sticks and baseball bats, that exhibits favorable vibration behavior and thus present no health risk to the player, and to do so without increasing the overall mass of the sports equipment or decreasing its strength. Moreover, it is the objective of this invention to provide a process that enables the manufacture of such a structural member.